1. Field of the Invention
The present invention relates to an integrated antenna coupler element, in particular for a multiband terminal of a mobile radio system.
2. Description of the Prior Art
Terminals in communications systems, in particular portable terminals such as mobile radio stations, are currently designed for maximum communications performance with minimum power consumption and are furthermore intended to be used as universally as possible. As such, at least for a specific market segment of such devices, they need to be designed for different transmission standards; particularly different transmission frequency bands.
For reasons of size, weight and cost, a single antenna is normally used in such devices, which then serves as both a receive and a transmit antenna for the frequency ranges for which the terminal is designed. This multiple use of the antenna requires special processing of the received signals and the signals to be transmitted, in order to ensure optimum utilization and interference suppression of the received signals, on the one hand, and minimum power consumption and extensive suppression of noise effects in transmit mode, on the other hand.
This is particularly relevant to terminals which operate in the xe2x80x9cconventionalxe2x80x9d GSM range, i.e. 900 MHz (more precisely: uplink in the 875 to 915 MHz frequency band and downlink in the 920 to 960 MHz frequency band) as well as to terminals which operate in the transmit/receive frequency range around 1800 MHz, often referred to as the PCN or DCS range, since harmonic effects can be particularly critical for such devices due to the approximate frequency ratio of 1:2. This must be taken into account through suitable filtering of the entire received signal, especially in receive mode in the GSM range, and through maximum suppression of the transmission of the first harmonic in GSM transmit mode.
In a dual-band terminal for GSM and DCS (PCN), separate pre-amplifiers for the GSM range and the DCS range, and normally also separate transmit output stages for the GSM and the DCS range, are provided in the receive component. The (entire) received signal from the antenna must be forwarded in the receive or monitor time slot, depending on the selected operating frequency band, either to the GSM pre-amplifier or to the DCS pre-amplifier, whereas the output signal of the GSM or DCS output stage must be fed to the antenna in the transmit time slot.
In receive mode in the GSM band, the antenna signal is fed via an antenna switch (if necessary with a diplexer) to a narrowband filter, in most cases designed as a surface acoustic wave (SAW) filter, through which it passes to be forwarded to the input of the GSM input amplifier (LNA=Low Noise Amplifier). For reception in the DCS band, the antenna signal is likewise fed via an antenna switch (again, if necessary, with a diplexer) to a narrowband DCS receive filter, in most cases designed as a ceramic filter, through which it passes to be forwarded to the input of the DCS-LNA.
In transmit mode in the GSM band, the output signal of the GSM transmit output stage is fed to a coupler element, the extracted subsignal of which serves to control the transmit power via a control loop. The actual transmit signal, after passing through the coupler, is fed to a low-pass filter, through which it passes to be forwarded via an antenna switch (again, if necessary, with a diplexer) to the antenna. In transmit mode in the DCS band, the output signal of the DCS transmit output stage is fed in a similar manner to a (separate) coupler, the extracted subsignal of which again serves to control the transmit power, whereas the actual transmit signal is filtered with a low-pass filter and then fed via an antenna switch (if necessary with a diplexer) to the antenna.
To date, a multiplicity of discrete components have been used to implement these functions, requiring a relatively large amount of space and shielding and assembly outlay.
An object of the present invention, therefore, is to improve the design of a terminal of the aforementioned type in this functional domain in such a way that the space requirement and assembly outlay are reduced.
The present invention includes the technical instruction indicating a component which implements the complex functions in the antenna input/output coupling domain, which can be manufactured, encapsulated and shielded as a whole at low cost on the basis of a homogeneous technological concept, and which is assembled in one assembly operation. Along with an operating voltage connection, this component has a signal input/output for connection to the antenna, at least one signal input for connection to the transmit output stage(s), at least one received signal output for connection to the receive stage(s) and at least two control signal inputs for changeover between transmit and receive mode and for the required transmit power, and at least one control signal output for a control voltage which is to be fed to the transmit output stage(s).
In a preferred embodiment of a conventional dual-band terminal, separate transmit signal inputs are provided for a first and second transmit frequency band and/or separate received signal outputs for a first and second receive frequency band and a control signal input for the frequency band selection.
For a terminal in which separate transmit output stages are provided for the two frequency bands, the antenna coupler element also includes separate control voltage outputs for these transmit output stages. In a terminal in which the required values (xe2x80x9cPWR Rampxe2x80x9d) are defined separately, the antenna coupler element, in a further preferred embodiment, also includes two corresponding control signal inputs.
The antenna coupler element according to the present invention represents the structural unification of at least the functional units of a received signal band-pass filter, a transmit signal low-pass or band-pass filter, a transmit signal directional coupler, a transmit output stage power control loop with temperature compensation and a transmit/receive antenna changeover switch.
Especially in a dual-band terminal, the antenna coupler furthermore implements at least separate received signal band-pass filters for the first and second receive frequency band and/or separate transmit signal low-pass or band-pass filters for the first and second transmit frequency range and/or separate transmit signal directional couplers for the first and second transmit frequency range and/or separate power control stages for two transmit output stages, which generate the transmit signals in the first or second frequency band.
However, both the power control for the output stage(s) and the directional coupler function can be implemented in each case in an individual functional segment of the integrated antenna coupler element. The antenna switch function also can be implemented in a single switch area.
In a technologically preferred embodiment, the antenna coupler element is implemented using what is known as xe2x80x9cLTCCxe2x80x9d or xe2x80x9cmultilayerxe2x80x9d ceramic technology. The aforementioned specific solutions can be used to implement the individual functional segments.
Some of the functional units, in particular (if such a unit is provided) the diplexer, directional couplers and switching elements, elements of low-pass filters, the transmit output stage power controller and input amplifiers are advantageously implemented via LTCC technology directly in the corresponding ceramic multilayer substrate. This substrate furthermore serves as a motherboard to accommodate further functional units which are not implemented directly in the substrate, in particular the surface wave filter, the RF detector diode and, if necessary, operational amplifier units. Compared with the state of the art, this design produces a considerable cost saving even in the implementation of the individual functions. Additional advantages are created by the integration of additional shielding walls into the LTCC motherboard, effecting EMI shielding of the functional units which are sensitive in this respect not only in relation to one another but also in relation to external interference, and reducing electromagnetic emission. The shielding of the individual functional units and the entire functional complex is thereby substantially simplified and more economically designed.
Additional features and advantages of the present invention are described in, and will be apparent from, the following Detailed Description of the Preferred Embodiments and the Drawings.